View single post by Herb Kephart
 Posted: Thu Jun 18th, 2015 04:52 pm
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Herb Kephart



Joined: Thu Jul 19th, 2007
Location: Glen Mills, Pennsylvania USA
Posts: 5981
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Convex. (high in the center) Keeps the belt riding at the largest diameter.

Lots of theories for this, from those who think they know, but don't. It was discussed over 3 or 4 issues of Gas Engine magazine years ago, and a lot of ''experts'' contributed ''reasons'' that a 3 year old wouldn't believe. Finally, someone who knew wrote a lengthy letter involving trigonometry that made sense. The rest -- like myself at the time --  knew that it worked, just didn't know why.

The only exception to this is sometimes where two pulleys of the same diameter are next to each other on the same shaft, one spinning loose the other locked to the shaft with a key, and turns with the shaft. Belt runs through a fork close to the pair, that can shift the belt sideways. When the pulleys are flat in this case, the fork is relied to maintain belt/pulley alignment--at the expense of edge wear on the belt. When the moving belt is on the ''loose'' pulley, the shaft stands still. When shifted over to the ''tight'' pulley, the shaft is driven. This whole contraption forms a clutch-- so that the main shaft (usually in the ceiling) can turn all the time that the prime mover is running, while individual machines can be started and stopped as needed. All of this is shown, and described, at the lower left corner of Salada's last pix.

Unless the main drive shaft, and the driven one--with the clutch --  are perfectly parallel, problems with engagement and dis-engagement --as noted by Salada will happen. Difficult to maintain this alignment with vibration and frame movement, but unavoidable under the conditions shown.

Herb



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